Problem: During the cold winter months, a sheet of ice covers a lake near the Arctic Circle. At the beginning of spring, the ice starts to melt. The variable $s$ models the ice sheet's thickness (in meters) $t$ weeks after the beginning of spring. $s=-0.25t+4$ By how much does the ice sheet's thickness decrease every $6$ weeks?
Answer: The rate of change of the equation is $-0.25$, which means the thickness of the ice sheet is decreasing at a rate of $0.25$ meters per week. To find the decrease in thickness, we can multiply $0.25$ by $6$, the number of weeks. $0.25\, \dfrac{\text{meters}}{\cancel{\text{week}}} \cdot 6\,\cancel{\text{weeks}}=1.5 \text{ meters}$ The ice sheet's thickness decreases by $1.5$ meters every $6$ weeks.